In the recent years, a tape-shaped magnetic recording medium (hereinafter referred to as a tape) are required to be capable of being recorded in high density and providing high outputs. Concretely, it is required to improve magnetic layers of the medium, and make the tape thinner to be capable of recording for a long time, which includes making thinner a component layer comprising the magnetic layers and a non-magnetic support.
However, even if a high output is achieved by making improvements in magnetic layer, head touch failures are liable to occur and thereby the output is lowered as long as a thin non-magnetic support is used. Though a high-output capability is not easily compatible with decrease in tape thickness as mentioned above, many studies have so far been made to reconcile them. Particularly, enhancement of tape stiffness in transverse direction (hereinafter referred to as TD) is known as a useful means to prevent head touch failures and achieve high outputs in thin tapes, is studied in various manners.
For example, Japanese Ptent Publication open to Public Inspection (hereinafter referred to as Pat. O.P.I. Pub.) No. 146518/1992 proposes a magnetic recording medium having a total thickness of 11 .mu.m or less and comprising a polyethylene terephthalate support having a TD Young's modulus of 700 kg/mm.sup.2 or more and a machine direction (hereinafter referred to as MD) Young's modulus of 800 kg/mm.sup.2 or less.
Japanese Pat. O.P.I. Pub. No. 146519/1992 proposes a magnetic recording medium having a TD stiffness/MD stiffness ratio of 0.65 to 1.00.
Further, Japanese Pat. O.P.I. Pub. No.271010/1992 proposes a magnetic recording medium having a total thickness of 11.mu.m or less and comprising a polyethylene terephthalate support having a TD Young's modulus of 700 kg/mm.sup.2 or more and an MD Young's modulus of 450 to 720 kg/mm.sup.2.
The TD stiffness of a tape is expressed in Et.sup.3 when the TD Young's modulus of a tape is shown by E and the tape thickness by t. Accordingly, when E is kept constant, the TD stiffness sharply decreases as the tape becomes thinner. However, the methods proposed so far specify only the TD and MD Young's moduli or the strength balance of TD/MD, and do not specify at all the relationship between these factors and the tape thickness.
With the increasing demand for recording of higher density and longer time, the tape thickness will be reduced to 6 .mu.m or so in the near future. For that reason, there is demanded a technique to maintain a high outputting capability even in such a thin tape, or a technique to manufacture, without lowering the output, a tape with uniform magnetic layer structure even in a tape thickness of 6 to 13 .mu.m.